The present invention relates generally to power supplies for welders, and more particularly, to an improved transformer and method to magnetically control a welding power source.
The design and use of relatively constant current arc welders using series inductive reactance as a control element for single-phase and three-phase transformers or generators is known in the art. Generally, such systems are connected to commercially available, single- or three-phase, 50 to 60 Hertz, voltages and currents. For example, in one arc welding system the single- or three-phase output of a gasoline or diesel engine driven generator, which comprises a relatively constant alternating current (AC) terminal voltage, is connected in series to an AC inductor to provide electrical current for AC welding processes. Alternatively, the electrical current can be rectified for direct current (DC) welding processes.
Known three-phase series inductance-reactance control devices include a transformer comprising a transformer core, three primary windings or wire coils, three secondary windings, a divided control core, and a crank mechanism for separating portions of the divided control core. The transformer core is designed to conduct three-phase magnetic flux and has three inner portions that are each encircled by a primary winding. A three-phase voltage source is connected to and excites the primary windings. Three secondary windings surround each of the primary windings and conduct secondary output currents. The divided control core is magnetically coupled to the secondary windings and generally has a first E-shaped laminated portion with three extending members adjacent to three extending members of a second inverted E-shaped laminated portion. The two E-shaped portions have innermost mating surfaces that can be separated or moved towards one another by use of the crank mechanism, which permits an operator to select different weld currents.
The flow of current in the primary coils generates a magnetic flux in the transformer core that induces currents in each of the secondary windings. The, output current values from the secondary windings are a function of the size of the air gap between the extending members of the two E-shaped portions. For example, for smaller air gap lengths where the extending E-shaped members are close together, magnetic flux created by the secondary coils couples more to the E-shaped portions resulting in a higher inductive reactance for the secondary coils and less output current. That is, lower reluctances of the flux paths allow more of the three-phase secondary magnetic flux to be coupled to the control core. This larger amount of coupled secondary magnetic flux field increases the value of the series inductive reactance available for reducing the output voltage. For larger air gaps where at least one of the E-shaped portions are moved away from the other E-shaped portion, less magnetic flux from the secondary coils couples to the E-shaped portions decreasing the series inductive reactance and allowing an increased output current to flow.
Crank mechanisms comprising hand cranks connected to gear systems that can include threaded shafts are commonly used to vary the air gap between the two E-shaped plates due to their inexpensive cost. The hand crank is designed to adjust the air gap between each of the extending members of the two E-shaped plates a fixed amount with each turn of the hand crank using a standard thread shaft and gear arrangement. Problems arise with the use of such devices however due to a non-linear sensitivity of the output current relative to the air gap distance between the two E-shaped portions. The air gap distance increases or decreases a fixed distance for each turn of the hand crank resulting in a change in the total path reluctance of the control core. Since the relationship between the total path reluctance and the length of the air gap is highly non-linear, each turn of the hand crank causes non-linear changes to the secondary output current. This non-linear effect is most noteworthy at small air gaps where the output current is low. Operators however need more control over the output current at the lower end of the current spectrum. One solution may be to change the gear ratio to decrease sensitivity at the low end and provide a wider spectrum. The problem with this mechanical solution is that since the relationship between the air gap distance and the output current is non-linear, decreasing the sensitivity at the low end, creates excessive cranking at the higher end.
It would therefore be desirable to have an economical apparatus and method for decreasing sensitivity of turns of the crank handle to variations in the secondary output current.
The present invention provides an apparatus and method of magnetically controlling a welding power source that overcomes the aforementioned concerns.
The present invention includes a series inductance-reactance control apparatus for welding. The transformer includes a transformer core configured to support a magnetic flux and at least one primary winding connected to a single or multi-phase voltage source that excites one or more primary coils, producing a flux in the transformer core. Secondary windings, configured to generate secondary voltages and currents, are wound about each of the primary windings and are magnetically coupled to the magnetic flux in the transformer core. The transformer also includes an improved control core magnetically coupled to the secondary windings. The improved control core has two sections and is configured such that at least one core section is movable by a standard crank mechanism. The transformer and series inductive reactor has an output current that is less sensitive to changes in physical displacements of the core sections when adjusted by the crank mechanism. This enables more accurate output current settings and adjustments by an operator and provides an economical solution for improving adjustment sensitivity.
In accordance with one aspect of the present invention, an apparatus for magnetic control of a welding power source includes a transformer core, at least one primary coil wound around a transformer core, and at least one secondary coil wound around the primary coil. The invention further includes a control core having at least two core sections, each core section having a side edge and a mating edge with an angle other than a right angle formed therebetween, and wherein at least one of the core sections is moveable with respect to another core section.
In accordance with another aspect of the invention, a system for magnetically controlling a welding power source includes a welder having a transformer. The transformer has a transformer core configured to allow flow of magnetic flux. The transformer also includes a primary winding wound about the transformer core having an edge surface defined by the plane formed by the first complete coil turn, and a secondary winding wound about the at least one primary winding and the transformer core. The transformer further includes a control core having a pair of core sections configured to move with respect to one another and each having a mating surface. At least one of the mating surfaces is other than parallel to the plane of the edge surface.
In accordance with yet another aspect of the present invention, a method for controlling magnetic flux of a welding power source includes providing a transformer core configured to allow flow of magnetic flux, providing a voltage across at least one primary winding encircling the transformer core, and magnetically coupling at least one secondary winding to the transformer core. The method further includes the step of varying a gap width between mating surfaces of two core sections, each core section having a base and at least one extending member that is non-rectangularly-shaped. The two control core sections are magnetically coupled to the at least one secondary winding.
The present invention also includes an apparatus for magnetic control of a welder power source having a means for creating and allowing flow of magnetic flux, and a means for generating a secondary current from the magnetic flux. The apparatus further includes a means for adjusting the secondary current, and a means for decreasing sensitivity of the adjusting means to variations in the secondary current at a lower end of a current output spectrum.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.